Water fluoridation is a population health intervention used in Canada and the United States to control tooth decay. The safety of administering fluoride via public drinking water is uncertain. Recent human studies suggest that exposure to fluoride in drinking water may alter thyroid function, increase blood lead levels, lower IQ, and increase the risk of developing ADHD. Still, many of the human studies included groups who were exposed to higher levels of fluoride and they often lacked a comparison group or sensitive measures of behavior or learning. Given widespread exposure to fluoridated water, the US National Research Council concluded in a 2007 report that rigorous epidemiological research is urgently needed to address the controversy about the safety of this public health intervention. The aim of this study is to determine if prenatal and childhood exposure to fluoride impacts learning abilities and behavioral problems in young Canadian children, with particular emphasis on vulnerable populations. The present proposal will build upon an exceptional national pregnancy cohort study: ?Maternal-Infant Research on Environmental Chemicals? (MIREC). The MIREC cohort is ideally suited to address the research objectives because the requisite information (urine during pregnancy and child outcomes) was collected in a large sample that varied as a function of municipal water fluoridation. Fluoride concentrations will be measured using stored urine samples obtained from a sample of 1960 pregnant women living in ten large Canadian cities ? half of which add fluoride to municipal water. Out of 1207 participants who were approached, standardized questionnaires assessing behavioral outcomes are available for 898 children (74% of sample) living in select cities across Canada. In addition, standardized cognitive assessments, or IQ scores, are available for 610 of the children in the birth cohort. The study will also examine whether neurodevelopmental outcomes differ among children who ingested infant formula using fluoridated versus non-fluoridated water. Finally, we will examine whether serial urinary fluoride concentrations in pregnant women are higher in women who live in communities that fluoridate their municipal drinking water. The results of this study will inform public health officials and decision makers about ?real-time? fluoride levels of pregnant women living in fluoridated and non-fluoridated communities. It will also provide important information about whether fluoride exposure adversely impacts children?s behaviors or learning abilities. This information will direclty impact decision making concerning the safety of water fluoridation among vulnerable populations and is therefore an area of high